Corrosion electrochemical polarization

Cement coatings are usually applied as linings for water pipes and water tanks, but occasionally also for external protection of pipelines [7]. Cement is not impervious to water, so electrochemical reactions can take place on the surface of the object to be protected. Because of the similar processes occurring at the interface of cement and object and reinforcing steel and concrete, data on the system iron/ cement mortar are dealt with in this chapter taking into account the action of electrolytes with and without electrochemical polarization. To ensure corrosion protection, certain requirements must be met (see Section 5.3 and Chapter 19). 

The corrosion current density icoa is evaluated by the electrochemical polarization resistance method assuming that both the anodic and the cathodic partial currents obey the Tafel relation ... 

ELECTROCHEMICAL POLARIZATION STUDY OF CORROSION INHIBITORS IN Cu CMP SLURRY... 

Levesque A, Bouteville A (2001) Evaluation of corrosion behaviour of tantalum coating obtained by low pressure chemical vapour deposition using electrochemical polarization. J Phys IVI1 Pr3-915-920... 

Localized corrosion and stress corrosion may often be observed. Stress corrosion cracks usually initiate at pits in many systems. The role of pitting is to disrupt films that otherwise prevent the ingress of hydrogen (118, 119). Electrochemical polarization technique may be used to distinguish between SCC and HE mechanisms in high-strength steels in sodium chloride solutions (120). 

This chapter outlines the basic aspects of interfacial electrochemical polarization and their relevance to corrosion. A discussion of the theoretical aspects of electrode kinetics lays a foundation for the understanding of the electrochemical nature of corrosion. Topics include mixed potential theory, reversible electrode potential, exchange current density, corrosion potential, corrosion current, and Tafel slopes. The theoretical treatment of electrochemistry in this chapter is focused on electrode kinetics, polarization behavior, mass transfer effects, and their relevance to corrosion. Analysis and solved corrosion problems are designed to understand the mechanisms of corrosion processes, learn how to control corrosion rates, and evaluate the protection strategies at the metal-solution interface [1-7]. 

The droplet height varied between 400 and 1100 pm. The local corrosion rates were determined by EIS and electrochemical polarization measurements. An increase in corrosion rate was observed with decreasing electrolyte thickness below 800 pm. The increase of the corrosion rate was due to the decrease of the diffusion layer thickness, resulting in an increase in oxygen reduction rate. 

For RBP, a logarithmic current density range of 2.5 to 6 mA/cm was used, as shown in Figure 7.13. Treated samples at 60,100, and 120 N are shown, whereas the other samples are not shown because of crowdedness in the figure. Potentiostatic polarization measurements were carried out using a Radiometer Analytical model PGZ 100 potentiostat/galvanostat with VoltaLab software. The electrochemical parameters—corrosion potential corrosion current... 

Immersion tests provide no information about reaction mechanisms and often they require relatively long exposure times. Electrochemical tests do not have these drawbacks and they are therefore widely used in practice. In the following electrochemical polarization methods are presented that provide information on the rate of uniform corrosion under conditions where the rate is controlled by charge-transfer. Other electrochemical test methods will be presented in subsequent chapters. 

ASTM G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements— Corrosion rate equations and sample calculations are included. In this standard, corrosion rates are calculated from galvanic cell currents, polarization corrosion data (including Tafel extrapolations), and polarization resistance data. 

Corrosion test methods can be divided into electrochemical and non-electrochemical methods. Among the electrochemical techniques that have been used successfully for corrosion prediction are potentiodynamic polarization scans, electrochemical impedance, corrosion current monitoring, controlled potential tests for cathodic and anodic protection, and the rotating cylinder electrode for studies of velocity effects [3i,32]. Though not literally a test, potential-pH (Pourbaix) diagrams have been used as road maps to help understand the results of other tests. 

The various electrochemical techniques employed for corrosion rate measurements have been discussed in detail by Scully in Chapter 7 and extensively referenced. This chapter also highlights the many pitfalls encountered with the inteipretation of electrochemical polarization measurements. Some of these difficulties are generic to aU polarization techniques, while others are more germane to inhibition. These latter ones will be discussed in greater detail. 

In this section the utility and limitations of various direct current electrochemical polarization techniques for investigating corrosion in the presence of microorganisms will he discussed. The reader is referred to other sections of this manual for a description of the techniques themselves. 

Immersion testing wiU generate weight loss data, or corrosion current measurements can be obtained from stan-deird electrochemical polarization tests (see ASTM G 5, Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements see also Ref 27). Corrosion rates in millimeters per year (mpy) for titanium alloys can be calculated from sample weight loss data as follows ... 

Corrosion tests for hydraulic brake line fluid, as well as for motor oil, grease, and lubricants, are listed in Table 12. In addition, the effects of various fuels on materials have been of importance due to the effect of small amounts of water, which can become trapped in eureas such as the fuel tank [57]. Various additives to fuels can prevent corrosion effects and include inhibitor packages and small amounts of alcohol and aromatics. Recently, corrosion testing of ethanol fuels has been of interest because small amounts of water as well as other contaminants (chlorides) cause severe corrosion to occur [55]. Tests for fuels include electrochemical polarization and immersion tests (Table 12). 

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